Ensure _simple_lazy_clause bind names are fixed before cloning

Fixed a regression in 1.2 due to the introduction of baked queries for
relationship lazy loaders, where a race condition is created during the
generation of the "lazy clause" which occurs within a memoized attribute. If
two threads initialize the memoized attribute concurrently, the baked query
could be generated with bind parameter keys that are then replaced with new
keys by the next run, leading to a lazy load query that specifies the
related criteria as ``None``. The fix establishes that the parameter names
are fixed before the new clause and parameter objects are generated, so that
the names are the same every time.

Fixes: #4507
Change-Id: I605b824e028c87bc20ca8c2577227cdf6a591064
(cherry picked from commit d71f34cb2a28e8dfc410bc5bec68372be6d7c333)

diff --git a/doc/build/changelog/unreleased_12/4507.rst b/doc/build/changelog/unreleased_12/4507.rst
new file mode 100644 (file)
index 0000000..39b37b9
--- /dev/null
+++ b/doc/build/changelog/unreleased_12/4507.rst
@@ -0,0 +1,13 @@
+.. change::
+   :tags: bug, orm
+   :tickets: 4507
+
+   Fixed a regression in 1.2 due to the introduction of baked queries for
+   relationship lazy loaders, where a race condition is created during the
+   generation of the "lazy clause" which occurs within a memoized attribute. If
+   two threads initialize the memoized attribute concurrently, the baked query
+   could be generated with bind parameter keys that are then replaced with new
+   keys by the next run, leading to a lazy load query that specifies the
+   related criteria as ``None``. The fix establishes that the parameter names
+   are fixed before the new clause and parameter objects are generated, so that
+   the names are the same every time.

diff --git a/lib/sqlalchemy/orm/strategies.py b/lib/sqlalchemy/orm/strategies.py
index 0d805f903bfe16498de1e7ca9519a64ab5fcd992..38bfbcc59668e779800c21b1480e289190a9ddb8 100644 (file)
--- a/lib/sqlalchemy/orm/strategies.py
+++ b/lib/sqlalchemy/orm/strategies.py
@@ -587,6 +587,9 @@ class LazyLoader(AbstractRelationshipLoader, util.MemoizedSlots):
 
         def visit_bindparam(bindparam):
             bindparam.unique = False
+        visitors.traverse(criterion, {}, {"bindparam": visit_bindparam})
+
+        def visit_bindparam(bindparam):
             if bindparam._identifying_key in bind_to_col:
                 params.append(
                     (

diff --git a/test/ext/test_baked.py b/test/ext/test_baked.py
index d46bd6cf234d98487fbc654333e0ca36c53e8045..2ae33de896a9c0cba90e52a67404a571e1c0ef5c 100644 (file)
--- a/test/ext/test_baked.py
+++ b/test/ext/test_baked.py
@@ -1266,6 +1266,21 @@ class LazyLoaderTest(testing.AssertsCompiledSQL, BakedTest):
             ),
         )
 
+    def test_simple_lazy_clause_no_race_on_generate(self):
+        User, Address = self._o2m_fixture()
+
+        expr1, paramdict1 = (
+            User.addresses.property._lazy_strategy._simple_lazy_clause
+        )
+
+        # delete the attr, as though a concurrent thread is also generating it
+        del User.addresses.property._lazy_strategy._simple_lazy_clause
+        expr2, paramdict2 = (
+            User.addresses.property._lazy_strategy._simple_lazy_clause
+        )
+
+        eq_(paramdict1, paramdict2)
+
     # additional tests:
     # 1. m2m w lazyload
     # 2. o2m lazyload where m2o backrefs have an eager load, test